Effect of Hf and Ta on Creep Rupture Characteristics and Properties of Powder Metallurgy Ni-Based Superalloys
ZHANG Haopeng1,2, BAI Jiaming1,2,3, LI Xinyu1,2,3, LI Xiaokun1,2, JIA Jian1,2, LIU Jiantao1,2, ZHANG Yiwen1,2()
1 High Temperature Material Research Institute, Central Iron and Steel Research Institute, Beijing 100081, China 2 Gaona Aero Material Co. Ltd., Beijing 100081, China 3 School of Materials Science and Engineering, Northeastern University, Shenyang 110819, China
Cite this article:
ZHANG Haopeng, BAI Jiaming, LI Xinyu, LI Xiaokun, JIA Jian, LIU Jiantao, ZHANG Yiwen. Effect of Hf and Ta on Creep Rupture Characteristics and Properties of Powder Metallurgy Ni-Based Superalloys. Acta Metall Sin, 2025, 61(4): 583-596.
Hf or Ta is widely added to powder metallurgy (PM) Ni-based superalloys to improve their microstructure and mechanical properties. However, research on the mechanism by which Hf and Ta synergistically affect creep performance is lacking. In this study, the effect of Hf and Ta on the creep rupture characteristics and properties of PM Ni-based superalloys at a temperature range of 650-750 oC was studied at multiple scales using SEM, EBSD, and TEM. The results showed that Hf and Ta significantly prolonged the creep rupture time, reduced the minimum creep rate, and improved the operating temperature and creep strength. The types of fracture morphologies at various creep temperatures were consistent, the crack source area exhibited intergranular fracture, the crack propagation area exhibited mixed fracture, but the addition of Hf and Ta significantly reduced the fraction of the crack source area. Considering that the stacking fault energy increased with increasing creep temperature, the creep deformation mechanism changed from microtwin shearing at 650 oC to microtwin and superlattice stacking fault shearing at 750 oC. In addition, Hf and Ta increased the content of MC-type carbides, significantly reducing the density of annealing twin boundaries and effectively inhibiting the nucleation of secondary cracks. Hf and Ta refined the M23C6 phase on grain boundaries and discontinued its precipitation, thereby strengthening the grain boundary and inhibiting the intergranular fracture. Hf and Ta reduced the stacking fault energy at various creep temperatures and increased the density of deformed microtwins, thereby increasing the resistance to dislocation movement. Moreover, Hf and Ta increased the volume fraction and average size of the secondary γ′ phase and increased the lattice mismatch between the γ and γ′ phases, thereby enhancing the strengthening effect of the γ/γ′ phase interface.
Table 1 Actual compositions of four kinds of experimental powder metallurgy (PM) Ni-based superalloys
Fig.1 Morphology of powders obtained by plasma rotating electrode process (PREP) (Inset shows one typical PREP powder) (a), the size of ingot after hot isostatic pressing (HIP) and heat treatment (HT) (unit: mm) (b), and the size of creep specimen (unit: mm) (c)
Fig.2 Microstructures and element distributions of 0Hf + 0Ta (a1-a3), 0.5Hf + 0Ta (b1-b3), 0Hf + 2.4Ta (c1-c3), and 0.5Hf + 2.4Ta (d1-d3) alloys (a1-d1) distributions of MC carbides (PPB—prior particle boundary) (a2-d2) morphologies of γ′ phase (a3-d3) element distribution mappings of γ and γ′ phases (HAADF—high angle annular dark field)
Fig.3 Stereoscopic images of the fracture morphologies of the alloys under different creep conditions of 650 oC, 970 MPa (a1-a4),700 oC, 770 MPa (b1-b4), and 750 oC, 580 MPa (c1-c4), showing the area fraction of crack source area (CSA) (CPA—crack propagation area) (a1-c1) 0Hf + 0Ta (a2-c2) 0.5Hf + 0Ta (a3-c3) 0Hf + 2.4Ta (a4-d4) 0.5Hf + 2.4Ta
Fig.4 Fracture morphologies of the CSA (a1-c1), the boundaries of CSA and CPA (indicated by the dotted yellow line) (a2-c2), and the CPA (a3-c3) of 0Hf + 0Ta alloy
Table 2 Creep rupture time (tr) and minimum creep rates () of the alloys under various creep conditions
Fig.6 Larson-Miller curves of alloys with varying Hf and Ta contents (Larson-Miller parameter LMP = , T is the temperature)
Fig.7 Bright-field (BF) TEM images, selected area electron diffraction (SAED) patterns, and dark-field (DF) TEM images of microstructures of the alloys after creep rupture at 650 oC, 970 MPa (D-MT—deformation microtwin) (a) 0Hf + 0Ta (b) 0.5Hf + 0Ta (c) 0Hf + 2.4Ta (d) 0.5Hf + 2.4Ta
Fig.8 TEM images of microstructures of 0Hf + 0Ta and 0.5Hf + 2.4Ta alloys after creep rupture at 750 oC, 580 MPa (The yellow arrows indicate D-MTs and the green arrows indicate superlattice stacking faults (SSFs)) (a) TEM image of 0Hf + 0Ta alloy (b) TEM image of 0.5Hf + 2.4Ta alloy (c) high-resolution TEM image of deformation microtwins (Inset shows the corresponding fast Fourier transform (FFT)) (d) TEM image of SSFs
Fig.9 Effects of Hf and Ta addition on the density of annealing twin boundaries (A-TB) of HT alloys (θ—misorientation) (a) 0Hf + 0Ta (b) 0.5Hf + 0Ta (c) 0Hf + 2.4Ta (d) 0.5Hf + 2.4Ta
Fig.10 Secondary cracks of 0Hf + 0Ta alloy after 650 oC, 970 MPa (a), 700 oC, 770 MPa (b), and 750 oC, 580 MPa (c) creep ruptures; and BF TEM image of an annealing twin (A-T) after 650 oC, 970 MPa creep rupture (d) (Inset in Fig.10d shows the corresponding DF TEM image; the blue arrows indicate A-TB, and the red circles indicate the sources of secondary cracks)
Fig.11 M23C6 phase on grain boundaries after 750 oC, 580 MPa creep rupture (Yellow lines indicate M23C6 phase) (a) 0Hf + 0Ta alloy (b) 0.5Hf + 2.4Ta alloy (c) BF TEM image of M23C6 phase in 0.5Hf + 2.4Ta alloy (d) DF TEM image, SAED pattern, and EDS corresponding to Fig.11c
Alloy
650 oC
700 oC
750 oC
0Hf + 0Ta
113.4
117.0
120.6
0.5Hf + 0Ta
109.7
113.3
116.9
0Hf + 2.4Ta
96.1
99.7
103.4
0.5Hf + 2.4Ta
91.6
95.2
98.9
Table 3 Stacking fault energy of the alloys at different temperatures (JMatPro calculated value)
Alloy
f / %[16]
d / nm[16]
λ / nm
δ / %[16]
0Hf + 0Ta
39.5
112
50
0.049
0.5Hf + 0Ta
41.5
165
52
0.087
0Hf + 2.4Ta
44.3
167
56
0.129
0.5Hf + 2.4Ta
44.8
176
59
0.138
Table 4 Volume fraction (f), average diameter (d), and average spacing (λ) of secondary γ′ phase; and lattice mismatch of γ and γ′ phase (δ)in HT alloys[16]
Alloy
650 oC,
970 MPa
700 oC,
770 MPa
750 oC,
580 MPa
0Hf + 0Ta
a1
a2
a3
0.5Hf + 0Ta
0.93a1
0.94a2
0.94a3
0Hf + 2.4Ta
0.68a1
0.69a2
0.70a3
0.5Hf + 2.4Ta
0.64a1
0.66a2
0.67a3
Table 5 Calculated values of minimum creep rate of the alloys under various creep conditions
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